Abstracts

Rationale: Typically, default mode network (DMN) deactivations have been reported in patients with epilepsy associated with ictal and interictal activity. This network plays a role in cognitive processes and conscious rest and failure to suppress the DMN during a task is associated with poor performance. Here, we investigated a patient with focal epilepsy located in the precuneus, a key hub within the DMN. We used EEG-fMRI to compare areas involved in interictal epileptiform discharges (IEDs) and analysed the functional connectivity of the DMN during rest and an attentional task.Methods: A 17 y.o. male with drug resistant focal epilepsy was studied. Scalp EEG indicated ictal onset in the midline-right posterior electrodes. MRI showed a subtle abnormality in the right precuneus, which was confirmed as the ictal onset with intracranial EEG and post-surgically as focal cortical dysplasia type IIA. The patient had no reduction in seizures at 6 months. Four sessions of EEG-fMRI recordings were made using a 64-channel MRI-compatible EEG and 1.5T MRI. During 2/4 sessions a paradigm was shown with alternating blocks of a movie and a please wait screen. For the remaining sessions the patient was told to rest with eyes closed. The same EEG-fMRI protocol was repeated in 8 healthy controls. Three types of analyses were applied: A) Visually identified IEDs were entered into a general lineal model (GLM) using SPM8 (www.fil.ion.ucl.ac.uk) along with movement and cardiac confounds. IED-related BOLD responses were found with an F-test across all 4 sessions. B) The paradigm blocks were entered into a GLM using SPM8 along with movement and cardiac confounds. Attention-directed task responses were found in each individual and then entered in a random effects second level analysis to compare differences between the patient and controls. C) The DMN was separated using independent component analysis as implemented in FSL (www.fmrib.ox.ac.uk) and visually identified (based on spatial consistency with prior studies). The connectivity of the DMN was compared both between task blocks and between healthy controls and the patient with a dual regression analysis in FSL.Results: EEG-fMRI IED-correlated analysis revealed areas of significant (p<0.001 uncor.) BOLD signal change in the right precuneus that were concordant with the epileptic focus (Fig. 1). During the movie periods, the patient showed activation of the DMN in addition to the attention networks (Fig. 2) that was different to the control group (p<0.05 FWE). Functional connectivity of DMN in the patient was increased within the network and with other cognitive networks both during rest and the task.Conclusions: EEG-fMRI revealed a focus consistent with other localisation methods and also suggested a wider extent of FCD than was resected consistent with the outcome. In a patient with an abnormality in the right precuneus we observed an aberrant activation of the DMN network in response to a task. Characterization of the dysfunction of DMN in a patient with epilepsy in one of the key nodes of this network may help us to understand its role and relationship to IEDs.